Hi I am student as well as doing job I just want to ask how much masturbation is healthy and I am also suffering from nightfall?

M'bation is healthy. Excess, like in anything is probably not a good idea. Once/day is certainly not unhealthy. Nightfall will likely cease if you masturbate or find a sex partner. Nightfall is a healthy, normal release of semen at night.
Distraction... It seems like you are too concentrated in sexual fantasies. It is normal to have sexual desires and look for satisfaction, but be careful in not to become an obsessive habit that will take too much of your time. Try to do sports or to read material not related to sex. If you could look for spiritual activities, will help a lot.